Lymph Nodes, Anaplastic large-cell lymphoma, ALK Positive, ALK1 stain

Anaplastic large cell lymphoma (ALCL) is a T-cell (or null cell) lymphoma with large CD30-positive pleomorphic cells. The majority of these are positive for the anaplastic large cell lymphoma kinase (ALK+). This ALK positivity is most frequently due to chromosomal abnormalities involving 2p23 and the ALK gene

The challenging aspect of this case is the morphology. This case represents the small-cell variant, which comprise about 5-10% of ALK+ ALCL. The malignant cells are mainly small, with irregular nuclei. A minor population of "hallmark" cells can be present, and these tend to be perivascular. Immunohistochemistry shows uniform, strong positivity for CD30 and ALK.

25% of these cases transform to classic anaplastic large cell lymphoma, and the transformation is usually associated with death within a year.

This slide shows ALK1 stain. See Related Content for H&E and CD30 stains.